1. Field of the Invention
The present invention relates to a suspension system for anchoring wheels used for steering to a frame of a vehicle.
2. Description of the Prior Art
Hereinafter, a fore to aft direction of the vehicle is called a longitudinal direction, and a side to side direction of the vehicle is called a transverse direction. Also, a location near to a centerline of the vehicle is called an inside location and a location distant from a centerline of the vehicle is called an outside location.
There has been known a double pivot type suspension system for a vehicle. For example, Japanese Utility Model Laid-Open Publication No. 64-26507 shows such a type of suspension system. This type suspension system comprises a steering knuckle for supporting a wheel, and an upper arm and a lower arm respectively connecting an upper portion and a lower portion of the steering knuckle to a frame of a vehicle. At least one of the arms comprises two link members, each of which is pivotally connected to the frame at a respective one end thereof, and to the steering knuckle at a respective opposite end thereof.
In this type of suspension system, a kingpin axis, which is an axis around which a wheel used for steering is turned, extends through a cross point between the axis of the two link members. The kingpin axis moves in response to the movement of the cross point in a horizontal plane during steering of the vehicle. As a result, a kingpin offset, which is a transverse distance between the kingpin axis and a center of a contact surface between the wheel and the ground, varies as the kingpin axis moves.